On Jul 27, 4:16*pm, KD7HB wrote:
On Jul 27, 1:01*pm, Ned Simmons wrote:



On Mon, 27 Jul 2009 11:25:38 -0700 (PDT), KD7HB
wrote:

On Jul 27, 10:14*am, Ned Simmons wrote:
On Mon, 27 Jul 2009 10:03:46 -0700 (PDT), KD7HB
wrote:

One interesting thing I discovered long
ago is that the faster the water flows through a system, the less heat
transfer that occurs.

So maximum cooling occurs at zero flow? g

--
Ned Simmons

No, maximum heat transfer occurs.

I can imagine there may be specific regimes where increasing flow
reduces heat transfer, but I don't believe that it's true in general.

You then have to get that hot water
out to cool it and recycle it back to the engine. Look at the top/
bottom of a radiator. Many small, restricted openings to the cooling
tubes.

Been too long since the college physics class.

It's been 35+ years for me since I dealt with Messrs. Reynolds,
Prandtl and Nusselt, and 34 years since I forgot it all.

--
Ned Simmons

I was really hit with this a few years ago when we installed a 7 stage
convection oven at my plant for soldering surface mount printed
circuit boards. The last stage of the oven is a cooling stage cooled
by chilled water. I bought a 1 ton chiller and hooked it to the oven
using 1 inch rubber hoses that match the connections on the chiller.
The oven had 1 inch connections, but had reducers to about 1/4 inch.
It was a used oven.

Being one for more efficiency, I pulled the reducers and connected the
1 inch hoses. Guess what? No cooling, but the water really ran fast
through the unit. When I put the reducing fittings back on the oven
connection, a very slow flow of water came out, but lots of cooling
air now came out of the unit.

Paul

I'm not sure in which end of the process (heating the water, or
cooling the water) the problem really lies.
I'm guessing it's on the cooling-the-water stage.

I know that the hotter you get the water, the faster it will dump its
heat in the radiator (the bigger the temp change, the faster the
transfer), and more heat will be removed from the system, so it could
just be the 'cool the water' stage that's inefficient.

It's not really the flow rate that matters, but the delta-T on each
end, which is of course affected by the volume rate of flow.

And of course, the longer the water lingers in the radiator, the more
heat will be removed from it.


Dave